dmaengine: axi-dmac: add a check for devm_regmap_init_mmio

The driver misses checking the result of devm_regmap_init_mmio().
Add a check to fix it.

Fixes: fc15be39

 ("dmaengine: axi-dmac: add regmap support")
Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Reviewed-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Link: https://lore.kernel.org/r/20191209085711.16001-1-hslester96@gmail.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>